The peak is composed of
granite underlain by gray gabbro-diorite
laccolith and the sedimentary rocks it intrudes, deeply eroded by glaciers. The hot granite that intruded parallel to the sedimentary rock converted the mudstone and sandstone into
schist, a dark metamorphic rock. The steep, light colored faces are eroded from the tougher, vertically jointed granitic rocks, while the foothills and dark cap rocks are the sedimentary
country rock, in this case
flysch deposited in the
Cretaceous and later folded. The radiometric age for the quartz diorite is 12±2 million years by the
rubidium-strontium method and 13±1 million years by the
potassium-argon method. More precise ages of 12.59±0.02 and 12.50±0.02 million years for the earliest and latest identified phases of the intrusion, respectively, were achieved using
Uranium–lead dating methods on single zircon crystals. Basal gabbro and diorite were dated by a similar technique to 12.472±0.009 to 12.431±0.006 million years. Thus, magma was intruded and crystallized over 162±11 thousand years. ==Gallery==